1. Field of the Disclosure
This disclosure relates to generally to the field of surgery. More specifically, the disclosure relates to devices for off-pump surgery.
2. Background of the Invention
Over 3.4 million people die each year because of congestive heart failure, a condition that often cannot be treated with drug or surgical therapies. For most patients that suffer heart failure, the best option is heart transplantation via an organ donor or by artificial means. The scarcity of suitable donor hearts (<2,000 per year) has left patients and doctors with no choice but to look to artificial heart therapies. This has been a prime motivating factor in the development of a total artificial heart (TAH). Although a reliable TAH has yet to be developed, great strides have been made in the development of implantable left ventricular assist devices (LVADs). Instead of totally replacing heart function, an LVAD supports the failing left ventricle by pumping blood from the left atrium or ventricle into the systemic circulation. LVADs have provided a well accepted means of stabilizing patients with heart failure until an acceptable donor has been procured.
Although current volume displacement or pulsatile LVADs have performed well clinically, their reliability after 18 months or so has been poor due to mechanical wear. These pumps utilize a pusher plate or diaphragm as well as inlet and outlet valves that result in pulsatile ejection not unlike the human heart. A pump that ejects 80 times per minute must eject 42 million times a year which presents a prohibitive design challenge for a mechanical system. As such, there has been interest in developing new types of pumps that do not rely on cyclic mechanical actuation. These efforts have resulted in the development of continuous flow pumps.
Continuous flow pumps offer several advantages over pulsatile pumps. Continuous flow pumps are generally smaller than pulsatile pumps and are more energy efficient. There is only one moving part, and many designs have no bearings or other components that are subject to mechanical wear. In addition, continuous flow pumps have the intrinsic ability to adjust pump output based on inflow and outflow pressure. These features make continuous flow pumps less likely to fail over time, and better suited for implantation in smaller patients.
A typical LVAD implantation procedure typically requires coring about a 2 cm hole in apex of the left ventricule. Before the apical hole is cored, the heart is elevated into position with laparatomy pads. The surgeon then cores the hole into the apex of the heart using either a coring tool or a scalpel. The surgeon then sutures an apical LVAD connector or cuff at the desired location on the ventricle such that a fluid tight connection is made. Once the LVAD connector is securely sutured to the left ventricle, the surgeon attaches the LVAD to the LVAD connector.
Traditionally, the patient is connected to a heart-lung machine, usually referred to as cardiopulmonary bypass, during the implantation procedure. Since the patient's blood is bypassed to the heart-lung machine, the pressure inside the left ventricle is significantly reduced. Thus, when the surgeon cores the hole from the left ventricular apex, minimal blood loss occurs and the surgeon has sufficient time to insert the LVAD's cannula into the LVAD connector.
However, though well tolerated by most patients, cardiopulmonary bypass constitutes a significant risk in the very ill and the very elderly. In patients with pre-existent organ dysfunction including organic brain disease, hepatic cirrhosis, renal insufficiency, and pulmonary insufficiency, CPB can cause significant morbidity or death. As patients with advanced heart failure not infrequently have co-morbid illnesses, avoiding cardiopulmonary bypass during LVAD insertion is attractive. As such, doctors have begun exploring surgical techniques without the use of the heart-lung machine i.e. off-pump surgery.
Off-pump LVAD implantation, however, presents substantial difficulties. For example, the surgeon is faced with the difficult task of operating on a moving heart. Further, the ventricle is positioned in the chest cavity behind the left breastbone. Repositioning the heart to make the ventricle more accessible while still permitting the heart to beat is not an easy task. Moreover, once positioned properly, the beating ventricle must be steadied in order to precisely suture the apical cuff or connector in place.
Coring a hole in the ventricle during off-pump surgery poses even greater difficulties. Because the patient is not on cardiopulmonary bypass, the heart is still responsible for maintaining the circulation. As such, the heart fills completely, generates high wall tension and cavity pressure, and ejects with each cardiac systole. Only by coring the apical plug in one swift move and inserting a finger, a plug, or the LVAD, can exsanguinating hemorrhage be averted and cardiac output maintained.
Another disadvantage to current off-pump surgical techniques is that it is difficult to ensure that the excised/cored heart tissue has been completely removed from the ventricle. For example, present surgical devices use an anvil in conjunction with a coring tool. These devices require making a cruciate incision in the ventricle and then inserting the anvil into the ventricle. Such a device not only causes unnecessary bleeding, but also does not provide an effective means of ensuring the complete removal of tissue.
Consequently, there is a need for surgical tools which allow a surgeon to implant ventricular assist devices without the use of a heart-lung machine i.e. off-pump. The surgical tools preferably should be simple to use and should minimize additional blood loss.